According to an embodiment, a crystal oscillation circuit comprises two capacitors connected between input and output terminals of a crystal oscillator and the ground, and a CMOS inverter coupled in parallel with the crystal oscillator. In such a crystal oscillation circuit, a sine wave is generated by the resonance of the crystal oscillator and the two capacitors. The CMOS inverter amplifies the sine wave and the crystal oscillation circuit outputs a current following the amplified sine wave. A large through current, however, flows through the CMOS inverter.
There are known methods for reducing power consumption due to the through current of such an inverter, such as providing a step-down circuit and a level shifter, as disclosed in, for example, Japanese Patent No. 3259528.
However, such methods are only capable of obtaining a current reducing effect from the voltage drop caused by the step-down circuit. These methods are not capable of controlling the through current of the inverter.